Problem: Solve for $x$ and $y$ using substitution. ${2x+6y = -4}$ ${x = -5y-8}$
Answer: Since $x$ has already been solved for, substitute $-5y-8$ for $x$ in the first equation. ${2}{(-5y-8)}{+ 6y = -4}$ Simplify and solve for $y$ $-10y-16 + 6y = -4$ $-4y-16 = -4$ $-4y-16{+16} = -4{+16}$ $-4y = 12$ $\dfrac{-4y}{{-4}} = \dfrac{12}{{-4}}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = -5y-8}\thinspace$ to find $x$ ${x = -5}{(-3)}{ - 8}$ $x = 15 - 8$ ${x = 7}$ You can also plug ${y = -3}$ into $\thinspace {2x+6y = -4}\thinspace$ and get the same answer for $x$ : ${2x + 6}{(-3)}{= -4}$ ${x = 7}$